JPH03100576A - Developing device - Google Patents

Abstract

PURPOSE:To obtain an image being free from ghost and fog and having sufficient density without generating a leakage of a magnetic particle by using a mixture of magnetic particles whose particle size distribution, magnetization or density, etc., are different from each other. CONSTITUTION:The device is provided with a non-magnetic developing sleeve 2 installed so as to be freely rotatable in a developing container 5 in which a two-component developer 10 consisting of a magnetic particle 6 and a toner 7 is contained, a non-magnetic material elastic blade 4 provided on the developing sleeve 2 so as to come into contact therewith, and a magnet 3 installed so as to be immovable in the sleeve 2. The magnet 3 has magnetic poles N, S, and in the vicinity of the surface of the developing sleeve 2 in the developing container 5, the magnetic particle 6 of the two-component developer 10 is held by magnetic force of the magnet 3. Also, two kinds or more of different magnetic particles, that which, are different in at least one of a particle size distribution, magnetization sigma or density(d) are used as the magnetic particle 6. In such a way, an image being free from ghost and fog and having sufficient density can be obtained without generating a leakage of the magnetic particle 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device used to develop an electrostatic latent image in an image forming apparatus using electrophotography, electrostatic recording, or the like.

[i string I] In image forming apparatuses that utilize electrophotography, electrostatic recording power, etc., dry type - Various developing devices using component developers have been proposed and put into practical use.

However, in any of the developing devices, it is extremely difficult to form a thin layer of dry component developer on the developer carrier, and only a relatively thick developer layer is formed.

However, as improvements in the clarity and resolution of developed images are currently being sought, it is essential to develop a method for forming a thin layer of a dry component developer and an apparatus therefor.

As a method of forming a thin layer of a conventionally known dry component developer, Japanese Patent Application Laid-Open No. 54-43037 has been proposed and has been put into practical use.

However, this is related to the formation of a thin layer of magnetic developer, and in order to make magnetic developer magnetic, it is necessary to add a magnetic substance internally, and for this reason, the developed image transferred to transfer paper cannot be thermally fixed. In addition, because the developer itself contains a magnetic material (Fii material is usually black),
There are problems such as poor color reproduction.

The present applicant uses a two-component developer consisting of non-magnetic toner and magnetic particles as a developing device that is completely different from conventional ones. forming a magnetic brush of magnetic particles by the magnetic force of the magnetic field generating means upstream of the magnetic particle restraining member with respect to the moving direction of the surface of the image carrier, and restraining the magnetic brush by the magnetic particle restraining member; A developing device in which a thin layer of non-magnetic toner is formed on a developer carrier has already been proposed.

The developing device proposed by the present applicant enables development using only non-magnetic toner at the development position with the image carrier, and also enables color development.

However, in a developing device in which magnetic particles and toner are mixed only in the developing container, if fine magnetic particles are used to improve image quality or the agitation force is increased, the magnetic particles will come out from inside the developing container. There was a problem with the image leaking and disturbing the image quality.

In addition, in order to achieve high image quality and high stability, it is necessary to ensure a sufficient and uniform supply of toner to the developer carrier over a long period of time, and at the same time, it is necessary to provide sufficient and uniform triboelectricity to the toner. was there.

Furthermore, in order to simplify and reduce the cost of developing devices, there is a demand not only for high added functionality for magnetic particles (but also for the standardization of devices, and for various types of developing devices such as heat fixing toners and pressure fixing toners). Although there is a growing demand for adaptation to anti-inflammatory agents, there are still some problems that have not yet been addressed.

Therefore, in view of the above-mentioned current situation, it is an object of the present invention to ensure the restraint of magnetic particles by a magnetic particle regulating member made of a non-magnetic material and its stability, and to provide a non-magnetic particle with the optimum tribo and coating amount for the development conditions. A uniform thin layer of magnetic toner can be stably formed on the developer carrier over a long period of time without being affected by various environmental changes, eliminating ghosts and fogging without leakage of magnetic particles. It is an object of the present invention to provide a developing device that makes it possible to obtain images with sufficient density.

in order to The above object is achieved by the developing device of the present invention.

To summarize, the present invention includes installing a developer carrier that is endlessly movable opposite to an image carrier in a developer container containing a two-component developer consisting of non-magnetic toner and magnetic particles, and
A magnetic field generating means for forming a magnetic brush of the magnetic particles is provided in the developer carrier, and a magnetic particle regulating member made of a non-magnetic material for restraining the magnetic brush of the developer is moved to the developer carrier. The developing device is provided so as to be brought into contact with the magnetic particles from the opposite direction, and the developing device is characterized in that the magnetic particles are a mixture of two or more different types of magnetic particles. According to one aspect of the present invention, the magnetic particles have a small particle size distribution, magnetization σ1, or density d
Either is different.

1 liter of blood Examples of the present invention will be described in detail below.

FIG. 1 is a schematic diagram showing an embodiment of the developing device of the present invention.

As shown in FIG. 1, the developing device of this embodiment includes a developer container 5 containing a two-component developer 10 consisting of magnetic particles 6 and toner 7, and a developer rotatably installed in the developer container 5. A non-magnetic developing sleeve 2 as a carrier, an elastic blade 4 made of a non-magnetic material as a developer regulating member provided on the developing sleeve 2 so as to be in contact therewith, and the sleeve 2
It is equipped with a magnet 3 fixedly installed inside.

The magnet 3 has magnetic poles N and S, and near the surface of the developing sleeve 2 in the developing container 5, the magnetic particles 6 of the two-component developer 10 are supported by the magnetic force of the magnet 3. According to the present invention, the magnetic particles 6 are composed of a mixture of particles 6a with large magnetization σ1 and large density d (and small particle size) and particles 6b with small magnetization σ1 and small density d and large particle size. be done.

As the developing sleeve 2 rotates in the direction of arrow B, the magnetic particles 6 supported on the surface of the sleeve 2 are transported, and when they reach the vicinity of the elastic blade 4, the magnetic particles 6 are transferred to the blade 4.
It is peeled off from the surface of the sleeve 2. Thereafter, the separated magnetic particles 6 return to the bottom of the developer container 5 by the action of gravity, are again supported on the surface of the sleeve 2 by the magnetic force of the magnet 3, and are transported as the sleeve 2 rotates.

In this manner, the magnetic particles 6 within the developer container 5 perform the circular motion shown by the arrow C due to the rotational movement of the developer sleeve 2, the magnetic force of the magnet 3, and gravity. During the circulation movement, the magnetic particles 6 take in the toner 7 and while mixing,
The magnetic particles 6 are transported near the sleeve 2 and are transported to the surface of the sleeve 2, at the same time imparting an electric charge to the toner 7 due to friction. Furthermore, the magnetic particles 6 that are transported near the surface of the sleeve 2 are transferred to the toner 7 due to friction with the sleeve 2. It has the function of appropriately increasing the electrical charge of the sleeve 2 and at the same time applying the toner 7 to the surface of the sleeve 2. Therefore, in the present invention, the magnetic particles 6 are required in an amount sufficient to cause circulation, that is, in an amount of 1.0 to 5.0 g/cm per unit length of the developing sleeve 2. When the amount of magnetic particles 6 is less than 1.0 g/am, sufficient circulation of the magnetic particles 6 is not performed, and on the other hand, when the amount exceeds 5.0 g/cm, the circulation speed becomes slow and the uptake of toner 7 is insufficient. Become.

The particle size of the magnetic particles 6 needs to be 30 μm or more. If it is less than this, it is difficult to completely peel off the magnetic particles 6 from the surface of the sleeve 2. However, 200
If it exceeds μm, the toner holding ability of the magnetic particles 6 will be small and sleeve ghost will easily occur, so the upper limit is 2.
It is necessary that the thickness be 00μ or less.

The elastic blade 4 has its proximal end supported by a support member 4a provided on the developer container 5, and its distal end surface pressed against the circumferential surface of the sleeve 2. A close contact area is formed. In this close contact area, the elastic blade 4 peels off the magnetic particles 6 of the developer 10 applied onto the developing sleeve 2 and allows only the toner 7 to pass through.

The elastic blade 4 may be brought into pressure contact with the developing sleeve 2 at the edge corner of its tip, or may be brought into pressure contact with the belly surface of the tip. However, if the edge angle of the tip is pressed against the surface of the sleeve 2, the magnetic particles 6 will leak out and have a negative effect on the image quality. It is necessary to set the edge angles so that they are in contact with each other at the same time as they are brought into pressure contact.

Further, as shown in the figure, the pressure contact mode of the elastic blade 4 is such that the gap between the elastic blade 4 and the circumferential surface of the sleeve 2 is inclined so that it gradually increases forward in the rotational direction of the developing sleeve 2. There are reverse pressure welding (counter pressure welding) and forward pressure welding that is inclined to gradually decrease in the opposite direction. In addition, the magnetic particles 6 and toner 7 accumulate and the magnetic particles 6 tend to leak (this is why it is preferable to use pressure welding in the opposite direction).

As described above, the thin layer of only the toner 7 applied and formed on the surface of the developing sleeve 2 is conveyed by the rotation of the sleeve 2 to the developing position 9 with respect to the photosensitive drum 1, where it is used as an image carrier. The electrostatic latent image formed on the photosensitive drum 1 rotating in the direction is developed. The toner 7 on the developing sleeve 2 flies to the photosensitive drum 1 and adheres to the electrostatic latent image.
The electrostatic latent image is developed and visualized as a toner image.

The gap between the photosensitive drum 1, which is the electrostatic latent image carrier, and the developing sleeve 2 is 50 to 500 μm, preferably 200 μm.
~400 μm. It has been experimentally confirmed that with a gap of this size, a toner image without fog and with high resolution can be formed by development. Further, during development, a bias electric field is formed between the photosensitive drum 1 and the sleeve 2 by the bias power supply 8 to perform development. As the bias to be applied, a direct current bias or a bias obtained by superimposing alternating current on direct current is used.

The remaining toner that was not subjected to development after passing through the development position 9 is
As the developing sleeve 2 rotates, it returns to the developing container S,
It is stripped off by the circulating magnetic particles 6, passes through the blade 4 again together with newly supplied toner 7, and is subjected to development.

In the present invention, as a method for regulating the magnetic particles 6, the elastic blade 4 made of a non-magnetic material is used as described above.
One feature is that it does not use magnetic force. When regulation is performed by magnetic force using a magnetic blade as in the past, an immobile layer of magnetic particles (a layer in which magnetic particles accumulate and do not move) is created in the regulation part, and as a result, the circulation area of magnetic particles is small. As a result, the toner is not sufficiently supplied to the sleeve, leaving the previous document pattern behind and causing a so-called ghost phenomenon.Furthermore, once the toner is applied, it is strongly pressed as it passes through the immovable layer, so it becomes charged. There were disadvantages in that the charge became too high and a sufficient concentration could not be obtained, especially in a low humidity environment.

In the present invention, since the elastic blade 4 made of a non-magnetic material is used and is not regulated by magnetic force, it is possible for the magnetic particles 6 to form a large circulation path without a stagnation part up to the vicinity of the elastic blade 4 of the regulation member. Therefore, since a sufficient amount of toner 7 is supplied and the applied toner 7 is constantly replaced, the applied toner 7 has an appropriately suppressed charge. Therefore, ghost phenomena and concentration decreases under low humidity do not occur.

The above-mentioned elastic blade 4 is used as a magnetic particle regulating member, and it is preferable to select a material for the blade 4 that will give the toner 7 the expected charge polarity when it rubs against the toner 7. For example, although it depends on the material of the toner 7, in order to positively charge a toner whose main component is polystyrene, ethylene propylene, fluororubber, natural rubber, polychlorobutadiene, N, B, R, etc. may be used. good. Conversely, in order to charge the material negatively, silicone rubber, polyurethane, or styrene-butadiene rubber may be used.

In addition, the elastic blade 4 can be made of not only a rubber plate but also a metal plate with a high elastic modulus. When using rubber, it is preferable that the hardness of the rubber is 50 to 70 degrees according to JISA. If the hardness of the rubber exceeds 70° according to JIS A, the elasticity of the rubber becomes strong, and the pressure at the contact part of the elastic blade 4 with the developing sleeve 2 becomes too high, causing the sleeve 2 to
The layer thickness of the toner 7 on top becomes excessively thin, and sufficient image density cannot be obtained. On the other hand, if the angle is less than 50°, the elasticity of the rubber itself becomes weak, making it difficult to maintain sufficient pressure at the contact portion with the sleeve 2.

FIG. 2 is a schematic diagram showing another embodiment of the developing device of the present invention. In this embodiment, the conditions will be explained in more detail. Note that the same reference numerals in FIG. 2 as in FIG. 1 indicate the same members.

As the developing sleeve 2, the surface of an aluminum sleeve with a diameter of 20 mm was polished with #400 abrasive grains.
The magnet 3 has a magnetic flux density of 700 gauss at the N pole, and an S
A two-pole magnet with a pole magnetic flux density of 600 Gauss was used. Of the N and S poles of the internal magnetic poles of the magnet 3, the position θ2 of the N pole is the position of the N pole on the opposite side of the photosensitive drum 1 relative to the horizontal line ρ, where ρ is the horizontal line passing through the central axis of the developing sleeve 2. The position θ3 of the S pole was set to θ3=90° on the upstream side in the rotational direction of 2. Further, the position θ1 of the elastic blade 4 is 01=on the upper side of the sleeve 2 and upstream in the rotational direction of the sleeve 2 with respect to the vertical line m, where m is a vertical line passing through the central axis of the developing sleeve 2.
It was set at 5°.

The elastic blade 4 was made of urethane rubber (rubber hardness JIS A66°, thickness 1.2 mm).

Next, the magnetic particles 6 in this example will be explained.

It is desirable that the magnetic particles 6 have an average particle diameter of 30 to 200 μm, preferably 40 to 150 μm.

The smaller the particle size of the magnetic particles 6, the better the image quality, and is particularly good against ground blur and sleeve ghost. This is because as the particle size becomes finer, the surface area increases and the degree of contact with the developing sleeve 2 also increases, so that the triboelectric force applied to the toner 7 between the developing sleeve 2 and the magnetic particles 6 is sufficiently performed. This is because it becomes like this. On the other hand, if the magnetic particles 6 are made coarser, the toner 7 is taken in too much (too much), and the triboelectricity of the toner 7 is lowered, causing ground force blur.

However, when the magnetic particles are made as fine as 60 particles, the magnetic binding force of the magnetic particles 6 due to the magnetic field of the magnet 3 becomes smaller, which makes it easier for the magnetic particles 6 to leak out of the developer container 5 and causes uneven uptake of the toner 7. It becomes easy.

Therefore, in order to compensate for the shortcomings and take advantage of the strengths of both,
As the magnetic particles 6, it is preferable to use a mixture of magnetic particles 6a (average particle diameter dA) with a narrow particle size distribution and coarse magnetic particles 6b (average particle diameter ct,), which allows sufficient and uniform distribution of the particles to the magnetic particles 6. This makes it possible to simultaneously improve the ability to take in the toner 7 and impart triboelectric effects to the toner 7.

As the magnetic particles 6, the present inventors used magnetic particles with various particle size distributions that were created by classifying every 50 meshes between 100 meshes and 400 meshes using a standard sieve (based on JIS-28801). I made an image.

That is, MA: 100-150 mesh, average particle size 130
um;Me: 350-400 mesh, average particle size 40
Using particles classified by μm and coated with acrylic resin and fluororesin, these magnetic particles M A and M m were mixed at a weight mixing ratio of 5, with MA:M++ l = 1.4:1.1: 4. Experiments were conducted on four cases in which only M8 was used.

The result is that M A: M s is l:4>1:1
>M.

Only > 4:1 The former was better, and there were differences in image quality in terms of sleeve ghosting, fogging, durability, solid black followability, etc.

In other words, it was found that the stirring effect of the coarse magnetic particles to increase the toner uptake ability and the specific surface area increasing effect of the fine magnetic particles to improve the tribo-imparting ability play the main roles. It can also be seen that the effect of coarse magnetic particles appears at the same weight.

Toner 7 is a toner powder with an average particle size of 12 μm, consisting of 100 parts of a copolymer of styrene/acrylic resin and styrene-butadiene resin, and 5 parts of a perylene-based red pigment.
When 1.0% colloidal silica was added and used, about 0.8 mg/ml was deposited on the developing sleeve 2 due to the above-mentioned coating action.
A layer of only toner 7 with a uniform crrf was obtained. The amount of charge on this toner layer was measured by the blow-off method and was +12.
Values in μc/g were obtained. This is a sufficient value as the amount of charge.

The bias voltage applied between the photosensitive drum 1 and the developing sleeve 2 by the bias power supply 8 has a frequency of 1500 Hz,
AC voltage with a peak-to-peak voltage of 1400Vp-p
A superimposed DC current of 00V was used. The surface potential of the electrostatic latent image on the photosensitive drum 1 was set to 1540 V in the dark area and 1220 V in the bright area, and development was performed with the gap between the sleeve 2 and the photosensitive drum 1 set to 250 μm, and the reflection density was 1. A good red image of No. 1 could be obtained.

In the above embodiments, so-called regular development is described in which a toner image is formed in an area where electric charges exist on the photosensitive drum 1. However, the present invention also provides reversal development in which a toner image is formed in an area where electric charges are erased. Needless to say, it is equally effective when doing the following. In addition, the magnetic particles 6 were used by mixing the magnetic particles 6a and 6b with different physical properties, but the mixing ratio of these magnetic particles 6a and 6b may be changed, and the particle size of the toner 70 may be changed so that each magnetic particle 6a , 6b may be used.

As explained above, in the developing device of the present invention, the magnetic brush of magnetic particles formed on the developer carrier is restrained by the magnetic particle regulating member made of a non-magnetic material, and the developer carrier When forming a thin layer of toner on the toner, a mixture of magnetic particles with different particle size distribution, magnetization, density, etc. is used as the magnetic particles, so the restraint and stability of the magnetic particles are ensured, and the development conditions A uniform thin layer of non-magnetic toner with optimal tribo and coating amount can be stably formed on the developer carrier over a long period of time without being affected by various environmental changes. Images with sufficient density can be obtained without leakage of magnetic particles and without ghosts or fog.

3: Magnet 4: Elastic blade 5: Developing container 6.6a, 6b: Magnetic particles 7: Toner 8: Bias power supply 10: Two-component developer

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the developing device of the present invention. FIG. 2 is a schematic diagram showing another embodiment of the developing device of the present invention. 1: Photosensitive drum 2: Developing sleeve

Claims (1)

[Scope of Claims] 1) A developer carrier movable endlessly is installed opposite to the image carrier in a developer container containing a two-component developer consisting of non-magnetic toner and magnetic particles; A magnetic field generating means for forming a magnetic brush of magnetic particles is provided in the developer carrier, and a magnetic particle regulating member made of a non-magnetic material for restraining the magnetic brush of the developer is provided on the developer carrier in its moving direction. What is claimed is: 1. A developing device provided so as to abut from opposite directions, wherein the magnetic particles are a mixture of two or more different types of magnetic particles. 2) The developing device according to claim 1, wherein the magnetic particles have different particle size distributions. 3) The developing device according to claim 1, wherein the magnetic particles have different magnetizations σ_■. 4) The developing device according to claim 1, wherein the magnetic particles have different densities d.